Effect of Buffer Layer Design on Vertical GaN-on-GaN p-n and Schottky Power Diodes

We study verticalGaN p-n and Schottky power diodes with different buffer layer thicknesses grown on free-standing GaN substrates, using metalorganic chemical vapor deposition. High breakdown voltage of > 1 kV and low specific on-resistance of 3 m Omega.cm(2) are achieved on GaN p-n diode with 1 mu m buffer layer and 9 mu m drift layer without passivation or field plate. Detailed device analysis on GaN Schottky diodes indicates that buffer layer has significant impacts on the electrical properties of drift layer and thus device performances of GaN p-n diodes. A thicker buffer layer will significantly enhance the breakdown voltages of these devices, which is possibly due to the improved material quality of drift layers with reduced defect densities. Higher doping concentration in drift layer with thicker buffer layer will, however, lower breakdown voltage. More discussions reveal improving the material quality of drift layer plays amore dominant role in achieving high breakdown GaN-on-GaN p-n and Schottky diodes with increasing buffer layer thickness.